1. Field
The present invention relates to a control apparatus for braking valves for operating machines or the like.
2. Description of the Related Art
Many operating machines, such as fork-lift trucks, tractors, cranes and the like, envisage the possibility of controlling the transmission of the motion from the motor to the wheels electronically.
As the technician in the sector knows, these operating machines are equipped with a function called “inching” which allows the operator to reduce and control the speed of the operating machine by operating the brake pedal, thereby changing the transmission ratio.
During a first part of the stroke of the brake pedal, the “inching” function allows partializing the traction without operating the brakes.
More in particular, during the first part of the pedal stroke, the operator modulates the speed of the operating machine by adjusting the motion transmission speed, while in the second part of the stroke the further movement of the pedal involves the direct intervention of the brakes.
As the technician in the sector knows, the “inching” function is controlled by means of a control apparatus comprising:                a fluid valve which is suitable for controlling the braking system of the operating machine and which is equipped with at least a distribution cursor of the operating fluid connected to the brake pedal;        a potentiometer, in turn connected to the fluid valve or to the brake pedal, which is suitable for emitting an electric signal proportional to the movement of the brake pedal itself.        
The electric signal emitted by the potentiometer is sent to the electronic unit which controls the traction, which has the job of regulating the transmission speed according to the signal received from the potentiometer.
In the operating machines of known type, the connection between the fluid valve or the brake pedal and the potentiometer is of the mechanical type.
More in particular, the control apparatus comprises mechanical means for transmitting the motion from the fluid valve cursor or from the brake pedal to the potentiometer.
The potentiometer takes the motion directly from the fluid valve cursor and the mechanical means which transfer the motion to the potentiometer can be of the rotary or linear type.
In this embodiment, the mechanical means which transfer the motion comprise a drive shaft, driven in rotation around its own axis by the cursor of the fluid valve, which mechanically couples with an outside element exiting from the potentiometer.
The movement of the cursor is transferred by means of the drive shaft to the outside element of the potentiometer which consequently emits an electric signal that varies in accordance with the movement of the outside element itself.
These known control apparatuses do have a number of drawbacks.
In particular, they are not very reliable due to possible oil leaks that can occur from the braking valve to the potentiometer.
In fact, notwithstanding the fact that a seal gasket is fitted on the drive shaft, it may occur, during use, that leaks occur due to wear, wrong assembly, a defect in the seal itself or other causes.
The obvious consequence of such leaks is the malfunction of the potentiometer and, therefore, of the control apparatus itself.
Another drawback of known types of control apparatus is due to the friction produced by the seal gasket on the connection shaft and which, besides causing the wear of the gasket itself, makes the movements of the connection shaft difficult.
Another drawback consists in the high construction complexity, which results in a complex assembly phase and, therefore, high costs that affect the end price of the apparatus itself.
Another type of control apparatus for braking valves is described by WO 0243996, DE 10 2005 014414 and DE 10 2004 043152.
These documents describe the use of a signalling device directly associated in translation with the distribution cursor of the operating fluid and of a detection sensor for detecting the movements of the signalling device.
More in particular, WO 0243996, considered as the closest known art, describes a control apparatus having a signalling element directly associated with the distribution cursor of the operating fluid, and therefore it too moving in translation inside the relative liner, and a sensor arranged outside the liner itself and suitable for detecting the movements of the signalling device.
By means of the position of the signalling device detected by the sensor, it is therefore possible to identify the position of the cursor.
The sensor device extends, outside the cursor liner, for a stretch substantially equal to the entire stroke of the cursor itself.
The apparatus described in WO 0243996 also has a number of drawbacks.
This apparatus, in fact, is complicated in terms of construction.
The complexity of such apparatus is also due to its structural conformation and in particular to the positioning and extension of the sensor arranged outside the cursor liner. In fact, as anticipated above, such sensor extends for a stretch substantially equal to the stroke of the cursor itself and therefore has considerable overall dimensions.